Positive electrode sheet, lithium ion battery, and electric device

Abstract

The present application relates to a kind of positive plate, battery and electric device comprising the positive plate, belong to battery technical field.The present application positive plate includes positive current collector and the positive material that is compounded on the positive current collector, wherein positive material contains positive active material, and positive active material includes lithium iron manganese phosphate agglomerate and ternary material, by controlling the peak area ratio a of (211) crystal face and (131) crystal face diffraction peak in the XRD spectrum of positive active material, the mass ratio b of Ni element in positive active material and the ratio c of lithium iron manganese phosphate agglomerate and ternary material quality satisfy 0.004≤a×b×c<0.230, so that the battery containing the positive plate has low gas production and high safety performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a positive electrode, a lithium-ion battery, and an electrical device. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) is an upgraded material of lithium iron phosphate, possessing advantages such as a high operating voltage platform, large theoretical specific capacity, good thermal stability, good chemical stability, wide availability, and low cost, making it one of the mainstream cathode active materials currently being researched. LMFP agglomerates refer to secondary particles formed by the aggregation of two or more primary particles, exhibiting an agglomerated state. Compared to non-agglomerated primary LMFP particles, using LMFP agglomerates can improve the solid-phase transport capability of the cathode system, reduce battery impedance, and improve kinetic performance. However, Mn in LMFP agglomerates will dissolve during charging and discharging, especially when the Mn content in the cathode active material is high. This leads to increased defects in the cathode material, increased oxidation of the electrolyte, and increased susceptibility to gas generation in the battery, affecting battery performance and safety. Therefore, it is necessary to develop a technology to reduce the gas generation of the LMFP agglomerate system. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a positive electrode, a lithium-ion battery, and an electrical device, so that the battery containing the positive electrode has both low gas production and high safety performance.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a positive electrode sheet, comprising a positive current collector and a positive electrode material composited on the positive current collector, wherein the positive electrode material comprises a positive electrode active material, the positive electrode active material comprising lithium manganese iron phosphate agglomerates and ternary materials, and the positive electrode sheet satisfies the following:

[0005] 0.004 ≤ a × b × c < 0.230

[0006] Where a is the ratio of the peak area of ​​the (211) crystal plane to the (131) crystal plane in the XRD spectrum of the positive electrode active material, which is dimensionless;

[0007] b represents the mass percentage of Ni element in the positive electrode active material, which is dimensionless.

[0008] c is the dimensionless ratio of the mass of lithium manganese iron phosphate agglomerates to the mass of the ternary material.

[0009] In a second aspect, the present invention provides a lithium-ion battery, including the positive electrode plate.

[0010] Thirdly, the present invention provides an electrical device including the lithium-ion battery.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention combines LMFP aggregates with ternary materials and controls the peak area ratio of the (211) crystal plane and (131) crystal plane diffraction peaks in the XRD spectrum of the positive electrode active material, the mass ratio of Ni element in the positive electrode active material, and the mass ratio of lithium manganese iron phosphate aggregates to ternary materials to satisfy specific relationships, so that the positive electrode sheet can significantly reduce the gas production after being applied to the battery, while ensuring that the battery has high safety performance. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0014] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0015] In this invention, there are no particular limitations on the specific dispersion and stirring methods.

[0016] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0017] In this invention, expressions such as "first time" and "second time" are not used to limit the number of times.

[0018] Positive electrode film

[0019] This invention provides a positive electrode sheet, comprising a positive current collector and a positive electrode material composited on the positive current collector, wherein the positive electrode material comprises a positive electrode active material, the positive electrode active material comprising lithium manganese iron phosphate agglomerates and ternary materials, and the positive electrode sheet satisfies the following:

[0020] 0.004 ≤ a × b × c < 0.230

[0021] Where a is the ratio of the peak area of ​​the (211) crystal plane to the (131) crystal plane in the XRD spectrum of the positive electrode active material, which is dimensionless;

[0022] b represents the mass percentage of Ni element in the positive electrode active material, which is dimensionless.

[0023] c is the dimensionless ratio of the mass of lithium manganese iron phosphate agglomerates to the mass of the ternary material.

[0024] Both the (211) and (131) crystal planes are characteristic crystal planes of LMFP aggregates. The (211) crystal plane represents the manganese-poor phase, while the (131) crystal plane usually corresponds to the main phase of LMFP, which is close to the crystal structure of standard LiMnPO4 and is one of the typical characteristic peaks of the olivine structure. The relative content of the manganese-poor phase can be semi-quantitatively assessed by the ratio of the peak areas of the (211) and (131) crystal plane diffraction peaks. If this ratio decreases, it indicates that the relative content of the manganese-poor phase decreases and the relative content of the manganese-rich phase increases. The LMFP structure is closer to LiMnPO4, which increases the risk of manganese dissolution and thus increases gas production.

[0025] The addition of ternary materials introduces Ni ions into the positive electrode active material. Compared to Mn ions in LMFP aggregates, Ni ions exhibit stronger catalytic oxidation activity, which is beneficial for oxidizing protonated hydrogen, altering the gas production pathway, and generating absorbable gases such as CO and CO2, while reducing the generation of non-absorbable gases such as H2. This reduces gas production when the positive electrode is used in the battery. However, an excessively high Ni mass percentage (b) in the positive electrode active material can increase heat generation and safety risks. The mass ratio (c) of lithium manganese iron phosphate aggregates to ternary materials also affects gas and heat generation. As this ratio decreases, the relative content of ternary materials increases, which helps improve gas production. However, an excessively high ratio leads to increased heat generation and safety risks. Therefore, a balance between a, b, and c is crucial. If a × b × c is too small, the battery will produce too much gas; if a × b × c is too large, the battery will generate too much heat, reducing battery safety performance.

[0026] Determination of lithium manganese iron phosphate agglomerates: The agglomeration state of primary particles can be observed using scanning electron microscopy (SEM) images.

[0027] The value of the peak area ratio (a) of the (211) crystal plane and the (131) crystal plane diffraction peak in the XRD spectrum of the positive electrode active material can be adjusted by adjusting the ratio of LMFP agglomerates to ternary materials and the proportion of elements such as Fe and Mn in the LMFP agglomerate structure.

[0028] The present invention does not limit the method for detecting the peak area ratio (a) of the diffraction peaks of the (211) crystal plane and the (131) crystal plane in the XRD pattern of the positive electrode active material. Those skilled in the art can detect the peak area ratio (a) of the diffraction peaks of the (211) crystal plane and the (131) crystal plane in the XRD pattern of the positive electrode active material using conventional techniques. For example, the peak area ratio (a) of the diffraction peaks of the (211) crystal plane and the (131) crystal plane in the XRD pattern of the positive electrode active material can be detected using the following method:

[0029] Disassemble the empty lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and air dry it at room temperature with humidity ≤15%.

[0030] The positive electrode material is scraped off from the surface of the current collector and calcined at 450℃ for 6 hours to remove the binder and conductive agent, thus obtaining the positive electrode active material.

[0031] The obtained positive electrode active material is ground and sieved. A 320-mesh (approximately 40 micrometers) powder sample is placed in a high-resolution X-ray diffractometer (such as Rigaku's Uitima IV). The sample amount is not less than 5 mg to ensure signal intensity.

[0032] The test conditions were set as follows: copper target, scanning voltage of 40KV, current of 40mA, scanning range of 5-80°, scanning speed of 4° / min, and XRD calibration was performed using the silicon internal standard method.

[0033] After starting the X-ray source and recording the diffraction data, identify and calculate the ratio of S(211) to S(131) to obtain a, where S(121) and S(131) are the peak areas of the diffraction peaks of the (211) crystal plane and the (131) crystal plane in the XRD spectrum of the positive electrode active material, respectively.

[0034] In the XRD pattern, the diffraction peak at a diffraction angle of 2θ of 36.1±0.1° is the (121) crystal plane diffraction peak, and the diffraction peak at a diffraction angle of 2θ of 35.3±0.1° is the (131) crystal plane diffraction peak.

[0035] Increasing the mass percentage (b) of Ni in the positive electrode active material leads to a greater catalytic oxidation activity of Ni ions compared to Mn ions in LMFP aggregates. This facilitates the oxidation of protonated hydrogen, alters the gas production pathway, and generates absorbable gases such as CO and CO2, while reducing the production of non-absorbable gases such as H2. Consequently, the gas production is reduced when the positive electrode is used in a battery. However, Ni doping also raises concerns about battery safety. Higher Ni content increases the likelihood of heat generation, raising the risk of thermal runaway.

[0036] The mass ratio of Ni in the positive electrode active material (b) can be adjusted by changing the proportions of Ni, Mn and / or Co in the ternary material structure, and the ratio of LMFP aggregates to the ternary material.

[0037] This invention does not limit the method for detecting the mass percentage (b) of Ni element in the positive electrode active material. Those skilled in the art can detect the mass percentage (b) of Ni element in the positive electrode active material using conventional techniques. For example, the mass percentage (b) of Ni element in the positive electrode active material can be determined using inductively coupled plasma mass spectrometry (ICP-MS), for example:

[0038] Disassemble the empty lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and air dry it at room temperature with humidity ≤15%.

[0039] The positive electrode material is scraped off from the surface of the current collector and calcined at 450℃ for 6 hours to remove the binder and conductive agent, thus obtaining the positive electrode active material.

[0040] Take an appropriate amount (approximately 0.1 g) of the obtained positive electrode active material and dissolve it in aqua regia (i.e., a mixture of concentrated nitric acid and concentrated hydrochloric acid, with a volume ratio of 3:1, wherein the concentrated nitric acid contains 65%–68% HNO3 by mass and the concentrated hydrochloric acid contains 36%–38% HCl by mass). Heat until completely dissolved, and dilute to 50 mL to obtain the sample solution. Use an ICP-MS instrument (such as the Thermo Fisher Scientific iCAP PRO X) with a radio frequency power of 1200 W and a carrier gas flow rate of 0.9 L / min, and use Ni isotope characteristic mass number 60 as the detection target to analyze the sample solution. By comparing the response values ​​of the standard solution and the sample solution, the Ni content in the sample solution is calculated, and then the mass percentage of Ni element in the positive electrode active material is calculated accordingly.

[0041] This invention does not limit the method for detecting the mass ratio (c) of lithium manganese iron phosphate agglomerates to ternary materials. Those skilled in the art can detect the mass ratio (c) of lithium manganese iron phosphate agglomerates to ternary materials using conventional techniques. For example, the mass ratio (c) of lithium manganese iron phosphate agglomerates to ternary materials can be detected using energy dispersive spectroscopy (EDS), for example:

[0042] Disassemble the empty lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and air dry it at room temperature with humidity ≤15%.

[0043] Scrape off the positive electrode material from the surface of the current collector and obtain the mass fraction of elements such as P, Mn, Fe, Ni, Co, and Al (if any) in the positive electrode material by EDS.

[0044] Calculate the mass fraction of LMFP in the cathode material: The chemical formula of LMFP is usually LiMn. x Fe 1-x PO4, where x represents the molar percentage of Mn calculated based on the total molar amount of Mn and Fe in lithium manganese iron phosphate (LMFP). Since EDS yields a mass fraction, an approximate Mn / Fe molar ratio needs to be assumed (e.g., x = 0.5, meaning the molar amounts of Mn and Fe are equal, as an initial calculation value; the actual value may need adjustment based on the specific material). Based on the chemical formula and mass fraction, the total mass fraction of P, Mn, and Fe in LMFP is calculated. This can be done by multiplying the mass fraction of each element by its relative atomic mass ratio in the LMFP chemical formula (considering the number of atoms) and then summing the results.

[0045] Calculate the mass fraction of ternary materials in cathode materials: The chemical formula of ternary materials is usually LiNi. y Co z M (1-y-z) O2, where M is at least one of Mn and Al. Based on the mass fractions of Ni, Co, and Mn obtained from EDS (minus the Mn contribution from LMFP), and the chemical formula of the ternary material, the total mass fraction of Ni, Co, and Mn elements in the ternary material is calculated. Similarly, this requires multiplying the mass fraction of each element by its relative atomic mass ratio in the ternary material's chemical formula (considering the number of atoms), and then summing the results.

[0046] Finally, the total mass fraction of LMFP is divided by the total mass fraction of ternary materials to obtain the mass ratio of lithium manganese iron phosphate agglomerates to ternary cathode materials.

[0047] The peak area ratio of the (211) crystal plane to the (131) crystal plane diffraction peak in the XRD pattern of the positive electrode active material (a), the mass ratio of Ni element in the positive electrode active material (b), and the mass ratio of lithium manganese iron phosphate agglomerates to ternary materials (c) all affect the gas production and heat generation of the battery using the positive electrode sheet to varying degrees, and they have a certain degree of mutual influence. It is difficult to achieve both low gas production and low heat generation in the battery by controlling a single variable. This invention controls the peak area ratio of the (211) crystal plane to the (131) crystal plane diffraction peak in the XRD pattern of the positive electrode active material (a), the mass ratio of Ni element in the positive electrode active material (b), and the mass ratio of lithium manganese iron phosphate agglomerates to ternary materials (c) to satisfy the above specific relationship, so that the gas production of the battery containing the positive electrode sheet is significantly reduced, while ensuring that the battery has high safety performance.

[0048] For example, the value of a×b×c can be selected as 0.004, 0.006, 0.008, 0.010, 0.025, 0.030, 0.045, 0.050, 0.065, 0.070, 0.085, 0.090, 0.105, 0.110, 0.125, 0.130, 0.145, 0.150, 0.165, 0.170, 0.185, 0.190, 0.205, 0.210, 0.225 or any range formed by any two of the above values.

[0049] In one preferred embodiment, the positive electrode sheet satisfies: 0.044 ≤ a × b × c < 0.110. Controlling the value of a × b × c within this specific range better balances the gas production and safety performance of the battery.

[0050] In some embodiments, the peak area ratio (a) of the diffraction peaks of the (211) crystal plane and the (131) crystal plane in the XRD spectrum of the positive electrode active material is in the range of 0.04 to 0.99, such as 0.04, 0.08, 0.10, 0.20, 0.35, 0.40, 0.55, 0.60, 0.75, 0.80, 0.95, 0.99 or any two of the above values.

[0051] In one preferred embodiment, the peak area ratio (a) of the diffraction peaks of the (211) crystal plane and the (131) crystal plane in the XRD spectrum of the positive electrode active material ranges from 0.32 to 0.99.

[0052] When the peak area ratio (a) of the (211) crystal plane and the (131) crystal plane diffraction peak in the XRD spectrum of the positive electrode active material is in the range of 0.04 to 0.99, especially in the range of 0.32 to 0.99, the gas production can be reduced while ensuring high energy density.

[0053] In some embodiments, the mass percentage (b) of Ni element in the positive electrode active material ranges from 0.004 to 0.440, such as 0.004, 0.006, 0.008, 0.010, 0.035, 0.050, 0.075, 0.100, 0.125, 0.140, 0.165, 0.180, 0.205, 0.220, 0.245, 0.260, 0.285, 0.300, 0.325, 0.340, 0.365, 0.380, 0.405, 0.420, 0.440, or any range formed by two of the above values.

[0054] In one preferred embodiment, the mass percentage (b) of Ni element in the positive electrode active material ranges from 0.015 to 0.350.

[0055] When the mass ratio (b) of Ni element in the positive electrode active material is within the range of 0.004 to 0.440, especially within the range of 0.015 to 0.350, it can not only better reduce the gas production amount, but also ensure that the battery has better safety.

[0056] In some of the embodiments, the ratio (c) of the mass of the lithium iron manganese phosphate agglomerate to the mass of the ternary material is 0.010 to 99.000, such as 0.100, 0.500, 1.000, 5.000, 10.000, 20.000, 30.000, 40.000, 50.000, 60.000, 70.000, 80.000, 90.000, 99.000 or the range formed by any two of the above values.

[0057] In one of the preferred embodiments, the ratio (c) of the mass of the lithium iron manganese phosphate agglomerate to the mass of the ternary material is 0.428 to 32.000.

[0058] When the ratio (c) of the mass of the lithium iron manganese phosphate agglomerate to the mass of the ternary material is within the range of 0.010 to 99.000, especially within the range of 0.428 to 32.000, it is more conducive to the balance of gas production and heat production.

[0059] In some of the embodiments, the chemical formula of the lithium iron manganese phosphate agglomerate is LiMn x Fe 1-x PO4, where 0 < x < 1. x can be selected as 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99 or the range formed by any two of the above values. The lithium iron manganese phosphate agglomerate can either contain no doping elements or contain doping elements. The present invention has no limitation on the type of doping elements in the lithium iron manganese phosphate agglomerate. For example, the doping element includes but is not limited to at least one of V, W, Ti, and Mg; at the same time, the present invention also does not limit the content of the doping elements in the lithium iron manganese phosphate agglomerate. Exemplarily, the mass percentage content of the doping elements in the lithium iron manganese phosphate agglomerate is 0 to 1%. The lithium iron manganese phosphate agglomerate can either contain no coating material or be coated with a coating material on some or all of its surfaces. The present invention has no limitation on the type of the coating material in the lithium iron manganese phosphate agglomerate. For example, the coating material includes carbon (such as hard carbon and / or graphene, etc.), silicide (iron silicide (FeSi2), manganese silicide (MnSi2)), metal oxide (aluminum oxide (Al2O3), titanium oxide (TiO2), zinc oxide (ZnO)) at least one of them; at the same time, the present invention also does not limit the content of the coating material in the lithium iron manganese phosphate agglomerate. Exemplarily, the mass percentage content of the coating material in the lithium iron manganese phosphate agglomerate is 0 to 1%.

[0060] In some embodiments, the particle size Dv50 of the lithium manganese iron phosphate agglomerates is 3 to 15 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any range formed by two of the above values.

[0061] This invention does not limit the method for detecting the particle size Dv50 of LMFP aggregates. Those skilled in the art can detect the particle size Dv50 of LMFP aggregates using conventional techniques. An exemplary method for testing the particle size Dv50 of LMFP aggregates is as follows:

[0062] After the battery is depleted, the positive electrode sheet is disassembled and dried. 0.1-0.2g of positive electrode material powder is collected with a scraper. The obtained positive electrode material powder is photographed using a scanning electron microscope (SEM, EVO15, Zeiss tungsten filament electron microscope). The size of LMFP agglomerates in the positive electrode material powder in the SEM image is measured using MEARSURE NANO software. The size of LMFP agglomerate particles is collected using the diagonal line method. After the sample size reaches more than 100, the particle size distribution is statistically analyzed, and the particle size-related parameter of LMFP agglomerates, Dv50, is calculated.

[0063] In this invention, the preparation method of the lithium manganese iron phosphate agglomerates is not limited; those skilled in the art can prepare the lithium manganese iron phosphate agglomerates using conventional techniques. Exemplarily, the preparation method of the lithium manganese iron phosphate agglomerates includes the following steps:

[0064] The precursor of manganese iron phosphate and the lithium source are mixed, ground into powder, sintered for the first time, and then ground, sprayed and dried to obtain the intermediate product of lithium manganese iron phosphate.

[0065] The obtained lithium manganese iron phosphate intermediate was subjected to a second sintering and coating to obtain lithium manganese iron phosphate agglomerates.

[0066] The ferromanganese phosphate precursor contains Mn, Fe, and P in the target stoichiometric ratio (i.e., the ratio of these three elements in the ferromanganese phosphate precursor is the same as the ratio of these three elements in the obtained lithium iron phosphate agglomerates, and other similar expressions are analogous). The ferromanganese phosphate precursor can be obtained by methods known in the art, such as solid-phase methods, co-precipitation methods, or spray drying methods. As an example, the preparation method of the ferromanganese phosphate precursor includes the following steps:

[0067] Manganese, iron, and phosphorus sources are dissolved in deionized water in stoichiometric ratios. A suitable complexing agent is added, and a precipitant is added under stirring conditions to adjust the pH to 6.0–6.5. The reaction produces Mn. x Fe(1-x) PO4 precursor. Among them, manganese source includes but is not limited to manganese sulfate and manganese acetate, iron source includes but is not limited to ferrous sulfate and ferric chloride, phosphorus source includes but is not limited to phosphoric acid and ammonium phosphate, complexing agent includes but is not limited to oxalic acid, precipitant includes but is not limited to ammonia water, and precipitant is added.

[0068] For example, in the process of preparing the lithium manganese iron phosphate agglomerates, the lithium source used includes, but is not limited to, at least one of lithium hydroxide, lithium dihydrogen phosphate, lithium phosphate, lithium carbonate, lithium nitrate, lithium oxalate, lithium citrate, and lithium acetate.

[0069] In one embodiment, during the preparation of the lithium manganese iron phosphate agglomerates, the molar amount of Li in the lithium source can be selected from 1.02 to 1.08, such as 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, or any range formed by two of the above values, based on the total molar amount of Mn and Fe elements in the lithium manganese iron phosphate precursor.

[0070] In one embodiment, during the preparation of the lithium manganese iron phosphate agglomerates, the temperature of the first sintering can be selected as 500–650°C, the sintering time can be selected as 8–15 h, and the sintering atmosphere for the first sintering can be nitrogen. For example, the temperature of the first sintering can be 500°C, 550°C, 600°C, 650°C, or any range formed by two of the above values; the sintering time can be 8 h, 10 h, 12 h, 15 h, or any range formed by two of the above values.

[0071] In one embodiment, during the preparation of the lithium manganese iron phosphate agglomerates, the temperature of the second sintering can be selected as 600–1000°C, the sintering time can be selected as 12–24 h, and the sintering atmosphere for the second sintering can be nitrogen. For example, the temperature of the second sintering can be 600°C, 750°C, 900°C, 1000°C, or any range formed by two of the above values; the sintering time can be 12 h, 15 h, 18 h, 20 h, 24 h, or any range formed by two of the above values.

[0072] The present invention does not limit the grinding method in the process of preparing lithium manganese iron phosphate agglomerates using the manganese iron phosphate precursor, and conventional grinding methods such as ball milling or sand milling can be selected.

[0073] This invention does not limit the spraying equipment and spraying process used in the preparation of lithium manganese iron phosphate agglomerates using the aforementioned manganese iron phosphate precursor; conventional spraying processes can be selected. In some embodiments, the spraying process meets the following requirements: spraying pressure of 0.3-0.8 MPa and slurry solid content of 20%-50% (by mass).

[0074] In some embodiments, after the second sintering, the resulting lithium manganese iron phosphate agglomerates are further washed, dried, and crushed.

[0075] When preparing lithium manganese iron phosphate agglomerates, a certain amount of dopant element source (if any) can be added when mixing the lithium manganese iron phosphate precursor and the lithium source. The dopant element source can be at least one of titanium source (such as titanium oxide), magnesium source (such as magnesium carbonate), vanadium source (such as vanadium pentoxide), tungsten source (such as ammonium metatungstate), etc., to obtain LMFP agglomerates containing a certain amount of dopant element.

[0076] In the preparation of lithium manganese iron phosphate (LMFP) agglomerates, to achieve a second sintering coating, a coating material source can be incorporated into the intermediate lithium manganese iron phosphate product. The coating material source can be at least one of glucose, sucrose, polyethylene glycol, polyvinyl alcohol, etc., to obtain LMFP agglomerates with partial or complete surface coating. However, coating may not be performed.

[0077] In some embodiments, the ternary material is selected from at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0078] In some embodiments, the ternary material has the chemical formula LiNi. y Co z M (1-y-z) O2,

[0079] Wherein, M is at least one of Mn and Al;

[0080] y is 0.2 to 0.95, such as 0.2, 0.3, 0.5, 0.8, 0.95 or any two of the above values ​​forming an interval;

[0081] z is 0.01 to 0.25, such as 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25 or any two of the above values ​​forming an interval.

[0082] The ternary material may contain or not contain doped elements. The present invention does not limit the type of doped element in the ternary material. For example, it may be selected as at least one of titanium, tin, tantalum, niobium, and lanthanide metals. At the same time, the present invention does not limit the content of doped elements in the ternary material. For example, the mass percentage of doped elements in the ternary material is 0 to 1%.

[0083] The ternary material may be free of coating material or may be coated with coating material on part or all of its surface. The present invention does not limit the type of coating material in the ternary material. For example, the coating material contains at least one element selected from the following: aluminum (Al), titanium (Ti), tungsten (W), boron (B), phosphorus (P), cobalt (Co), yttrium (Y), and silicon (Si). At the same time, the present invention does not limit the content of coating material in the ternary material. For example, the mass percentage of coating material in the ternary material is 0 to 1%.

[0084] The ternary material can be selected as primary particles, secondary particles (composed of two or more primary particles), or a mixture of primary and secondary particles.

[0085] In some embodiments, the particle size Dv50 of the ternary material is 1 to 20 μm, such as 1 μm, 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 17 μm, 20 μm or any range formed by two of the above values.

[0086] This invention does not limit the method for detecting the particle size Dv50 of ternary materials. Those skilled in the art can detect the particle size Dv50 of ternary materials using conventional techniques. An exemplary method for testing the particle size Dv50 of ternary materials is as follows:

[0087] After the battery is depleted, the positive electrode sheet is disassembled and dried. 0.1-0.2g of positive electrode material powder is collected with a scraper. The obtained positive electrode powder is photographed using a scanning electron microscope (SEM). The size of the ternary material in the positive electrode material powder in the SEM image is measured using MEARSURE NANO software. The size of the ternary material particles is collected using the diagonal line method. After the sample size reaches more than 100, the particle size distribution is statistically analyzed, and the particle size-related parameter of the ternary material, Dv50, is calculated.

[0088] In this invention, the preparation method of the ternary material is not limited, and those skilled in the art can prepare the ternary material using conventional techniques. For example, the preparation method of the ternary material includes the following steps:

[0089] The ternary material precursor and the lithium source are mixed and then sintered to obtain the ternary material.

[0090] The ternary material precursor contains Ni, Co, and M in a target stoichiometric ratio (i.e., the ratio of these three elements in the ternary material precursor is the same as the ratio of these three elements in the obtained ternary material, and other similar expressions are similar). The ternary material precursor is at least one of the oxides, hydroxides, and carbonates of Ni, Co, and M. For example, the ternary material precursor is a hydroxide of Ni, Co, and M.

[0091] The ternary material precursor can be obtained by methods known in the art, such as co-precipitation, gelation, or solid-state methods. As an example, the preparation method of the ternary material precursor includes the following steps:

[0092] Ni source, Co source and M source are dispersed in solvent to obtain a mixed solution;

[0093] The mixed solution, strong alkali solution, and complexing agent solution are simultaneously pumped into a stirred reactor. The pH of the reaction solution is controlled at 10–13, and the temperature inside the reactor is controlled at 25°C–90°C. During the reaction, an inert atmosphere (such as nitrogen or at least one of the inert gases) is introduced for protection. After the reaction is completed, the mixture is aged, filtered, washed, and vacuum dried to obtain hydroxides containing Ni, Co, and M, which is the precursor of the ternary material.

[0094] In the process of preparing the ternary material precursor, the Ni source used includes, but is not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate;

[0095] And / or, the Co source used includes, but is not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate;

[0096] And / or, the M source used includes at least one of Mn source and Al source. For example, the Mn source includes, but is not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate; the Al source includes, but is not limited to, at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride.

[0097] And / or, when dispersing Ni source, Co source and M source in a solvent, the solvent used includes, but is not limited to, water;

[0098] And / or, the base used in the strong base solution includes, but is not limited to, at least one of sodium hydroxide and potassium hydroxide;

[0099] And / or, the complexing agent solution used includes, but is not limited to, ammonia.

[0100] In the preparation of the ternary material precursor, the amounts of Ni source, Co source, and M source used can be selected to satisfy the following molar ratio: Ni molar ratio: Co molar ratio: M molar ratio = (92-10):(5-35):(3-85). By adjusting the proportion of Ni molar ratio in the Ni source to the total molar ratio of Ni, Co, and M elements contained in the Ni, Co, and M sources, the molar ratio of nickel in the ternary material structure can be controlled.

[0101] In the process of preparing the ternary material, the Li source used includes, but is not limited to, at least one of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium nitrate (LiNO3).

[0102] In the process of preparing the ternary material, the ratio of the amount of lithium source used to the amount of ternary material precursor used satisfies the following: molar amount of Li element: sum of molar amounts of Ni, Co and M elements = (1.05-1.2):1.

[0103] When mixing ternary material precursors and lithium sources, a ball mill or high-speed mixer can be used.

[0104] In the process of preparing ternary materials using ternary material precursors, the sintering atmosphere is an inert atmosphere, such as a nitrogen atmosphere, a helium atmosphere, or an argon atmosphere.

[0105] In the process of preparing ternary materials using ternary material precursors, the sintering temperature can be selected as 750-1000℃, and the sintering time can be selected as 8-20h.

[0106] When preparing ternary materials, a certain amount of dopant element source (if any) can be added when mixing the ternary material precursor and the lithium source. The dopant element source can be at least one of titanium source, tin source, niobium source, tantalum source, lanthanide metal element source, etc., to obtain ternary materials containing a certain amount of dopant element.

[0107] In the preparation of ternary materials, the ternary materials can also be coated as needed. Specifically, a dry coating method (high-temperature solid-state method) is used to coat the surface of the ternary material with a coating material, so that the surface of the ternary material is partially or completely covered with a coating layer formed by the coating material. For example, the coating layer contains at least one element selected from the following (hereinafter referred to as the "coating element"): aluminum (Al), phosphorus (P), silicon (Si), titanium (Ti), tungsten (W), boron (B), cobalt (Co), or yttrium (Y).

[0108] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode material is 80% to 98%, such as 98%, 96%, 94%, 92%, 90%, 88%, 86%, 84%, 82%, 80%, or any range formed by any two of the above values.

[0109] In addition to the aforementioned positive electrode active material, the positive electrode material also includes a conductive agent and a binder.

[0110] The conductive agent in the cathode material is used to provide conductivity. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent in the cathode material includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes. Carbon fibers include, for example, carbon nanofibers; carbon black includes, for example, SP (Super P), acetylene black, and Ketjen black.

[0111] In some embodiments, the mass percentage of the conductive agent in the positive electrode material is 0.1% to 5%, such as 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, or any range formed by any two of the above values.

[0112] The binder in the positive electrode material is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. For example, the binder in the positive electrode material layer includes, but is not limited to, fluorinated polyolefin binders, including but not limited to polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified derivatives (e.g., modified with carboxylic acids, acrylic acid, acrylonitrile, etc.).

[0113] In some embodiments, the mass percentage of the binder in the positive electrode material is 0.1% to 5%, such as 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, or any range formed by any two of the above values.

[0114] The cathode material can be composited on one side of the cathode current collector or on both sides of the cathode current collector.

[0115] The present invention does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: aluminum, nickel, titanium, stainless steel, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0116] The positive electrode sheet of this invention can be prepared according to conventional methods in the art. For example, a positive electrode active material, a conductive agent, and a binder are dispersed in a solvent to obtain a positive electrode slurry. The positive electrode slurry is then coated onto at least one side of a positive electrode current collector, and after processes such as drying, rolling, and slitting, a positive electrode sheet is obtained. The solvent used to prepare the positive electrode slurry includes, but is not limited to, at least one of N-methylpyrrolidone (NMP) and deionized water.

[0117] Battery

[0118] The present invention also provides a battery, comprising the positive electrode sheet, the negative electrode sheet and the electrolyte.

[0119] The negative electrode sheet of the present invention comprises a negative electrode current collector and a negative electrode material compounded on at least one surface of the negative electrode current collector, and the negative electrode material contains a negative electrode active material.

[0120] The present invention places no particular limitation on the negative electrode active material. Exemplarily, the negative electrode active material includes, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, SiO e (0 < e < 2, such as e = 1), silicon carbide, Li4Ti5O 12 and at least one of the above.

[0121] In some embodiments, the mass percentage content of the negative electrode active material in the negative electrode material is 80% to 99%, such as 99%, 96%, 94%, 92%, 90%, 88%, 86%, 84%, 82%, 80% or the range formed by any two of the above values.

[0122] The negative electrode material may further contain a conductive agent and / or a binder.

[0123] The conductive agent in the negative electrode material is used to provide conductivity, and any conductive agent can be used without particular limitation as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent in the negative electrode material includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fiber, activated carbon, mesoporous carbon, fullerenes, etc. Among them, carbon fiber such as carbon nanofiber, etc.; carbon black such as SP, acetylene black, Ketjen black, etc.

[0124] In some embodiments, the mass percentage content of the conductive agent in the negative electrode material is 0.1% to 5%, such as 0.1%, 0.5%, 1.0%, 2.0%, 4.0%, 5.0% or the range formed by any two of the above values.

[0125] The binder in the negative electrode material is used to improve the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector, and any binder can be used without particular limitation as long as it has suitable binding property and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder in the negative electrode material includes, but is not limited to, at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, aqueous acrylic resin.

[0126] In some embodiments, the mass percentage of the binder in the negative electrode material is 0.1% to 5%, such as 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, or any range formed by any two of the above values.

[0127] The negative electrode material can be composited on one side of the negative electrode current collector or on both sides of the negative electrode current collector.

[0128] The present invention does not impose any particular restrictions on the negative electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with at least one of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0129] The electrolyte of this invention can be any of the various electrolytes suitable for batteries in the art. The electrolyte comprises an electrolyte and a solvent, and the electrolyte typically includes a lithium salt.

[0130] For example, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be selected as 0.5–2 mol / L.

[0131] For example, the solvent includes, but is not limited to, at least one selected from ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The mass percentage of the solvent in the electrolyte can be selected as 75% to 85%.

[0132] In addition, the electrolyte may also contain additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance characteristics, such as triphenyl phosphate (TPP), dimethyl 2,5-dioxane carboxylate (DMOHC), etc., to improve high-temperature battery performance; terephthalic acid (PTMN), etc., to improve overcharge performance; and dimethyl sulfite (DMS), etc., to improve low-temperature battery performance. The mass percentage of the additives in the electrolyte may be selected from 0.1% to 2%.

[0133] The battery may further include a separator located between the positive and negative electrode plates to separate them and prevent short circuits caused by contact. The separator can be any suitable battery separator material in the art. Exemplarily, the separator includes, but is not limited to, at least one of polypropylene and polyethylene.

[0134] Electrical appliances

[0135] The present invention also provides an electrical device comprising the battery. The battery serves as the power supply for the electrical device.

[0136] The term "electrical device" refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other energy forms, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, and e-cigarettes; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0137] The present invention is further illustrated below with specific embodiments. It should be noted that, unless otherwise specified, the sintering is carried out in an air atmosphere:

[0138] Example 1

[0139] This embodiment provides a lithium-ion battery, and the specific preparation method is as follows:

[0140] (1) Preparation of positive electrode

[0141] (1.1) Preparation of ternary materials

[0142] Ni y Co z M (1-y-z) (OH)₂ and lithium hydroxide are added to a ball mill and ball-milled until powdered, with Ni being the most abundant component. y Co z M(1-y-z) Based on the sum of the molar amounts of Ni, Co, and Mn in (OH)₂, the molar amount of Li in lithium hydroxide was calculated to be 1.1. The lithium hydroxide was then sintered at 800℃ for 13 hours in a nitrogen atmosphere to obtain LiNi. y Co z M (1-y-z) O2, that is, the target ternary material, where the values ​​of y and z and the types of M elements are shown in Table 1.

[0143] (1.2) Preparation of LMFP aggregates

[0144] The precursor Mn of manganese iron phosphate x Fe 1-x PO4 and lithium hydroxide were added to a ball mill and ball-milled to a powder state. The total molar amount of Mn and Fe in the manganese iron phosphate precursor was used as the basis for calculation, and the molar amount of Li in the lithium source was 1.03. The mixture was then subjected to a first sintering at 600℃ for 10 hours. The sintered product was then ground, spray-dried, and subjected to a second sintering at 700℃ for 12 hours. After washing, drying, and crushing, the target LiMn was obtained. x Fe 1-x PO4 aggregates, where the values ​​of x are shown in Table 1.

[0145] (1.3) Preparation of positive electrode

[0146] The above-mentioned LMFP agglomerates and ternary materials were used as positive electrode active materials (the mass ratio of LMFP agglomerates and ternary materials is shown in Table 1). The positive electrode active materials, conductive agent acetylene black and binder PVDF were mixed at a mass ratio of 96:2:2, and solvent NMP was added. The mixture was stirred and dispersed under the action of a vacuum stirrer to obtain positive electrode slurry.

[0147] The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the positive electrode sheet is obtained.

[0148] (2) Preparation of negative electrode

[0149] Graphite, acetylene black, SBR binder and PAA binder were mixed in a mass ratio of 96:1:2:1, deionized water was added as solvent, and the mixture was stirred and dispersed under vacuum to obtain a negative electrode slurry.

[0150] The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the negative electrode sheet is obtained.

[0151] (3) Preparation of electrolyte

[0152] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 3:5:2 to obtain a mixed organic solvent. Dry lithium salt LiPF6 was then dissolved in the above mixed organic solvent, and dimethyl 2,5-dioxane carboxylate (DMOHC) was added to prepare an electrolyte with a LiPF6 concentration of 1 mol / L and a DMOHC mass percentage of 8.5%.

[0153] (4) Preparation of the separating membrane

[0154] A polyethylene (PE) diaphragm is used.

[0155] (5) Preparation of lithium-ion batteries

[0156] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare battery cell. The bare battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained. The specific formation steps are as follows:

[0157] The battery is pre-charged to 20% SOC using a constant current of 0.02C;

[0158] Charge to 80% SOC using a constant current of 0.33C;

[0159] Charge to 90% SOC using a constant current of 0.1C;

[0160] Charge to 4.25V with a constant current of 0.2C, then switch to constant voltage charging with a cutoff current of 0.05C.

[0161] Examples 2-26 and Comparative Examples 1-2

[0162] These examples and comparative examples all provide a lithium-ion battery, and the preparation method is similar to that of Example 1, except that:

[0163] (a) In step (1.1), the values ​​of y and z and the types of M elements are shown in Table 1;

[0164] (b) In step (1.2), the values ​​of x are shown in Table 1;

[0165] (c) In step (1.3), the mass ratio of LMFP aggregates to ternary materials is shown in Table 1.

[0166] Table 1

[0167]

[0168]

[0169] The following methods were used to detect the peak area ratio (a) of the (211) crystal plane to the (131) crystal plane diffraction peaks in the XRD spectra of the cathode materials in each embodiment and comparative example, the mass ratio of Ni element in the cathode active material (b), and the mass ratio of lithium manganese iron phosphate agglomerates to ternary materials (c). The test results are shown in Table 2:

[0170] (1) Detection of the peak area ratio of the (211) crystal plane to the (131) crystal plane diffraction peaks in the XRD spectrum of the positive electrode active material:

[0171] Disassemble the empty lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and air dry it at room temperature with humidity ≤15%.

[0172] The positive electrode material is scraped off from the surface of the current collector and calcined at 450℃ for 6 hours to remove the binder and conductive agent, thus obtaining the positive electrode active material.

[0173] The obtained positive electrode active material was ground and sieved. 8 mg of 320 mesh (about 40 micrometers) powder sample was placed in a high-resolution X-ray diffractometer (Rigaku's Uitima IV). The test conditions were set as follows: copper target, scanning voltage of 40 kV, current of 40 mA, scanning range of 5-80°, scanning speed of 4° / min. XRD was calibrated by silicon internal standard method.

[0174] After starting the X-ray source and recording the diffraction data, identify and calculate the ratio of S(211) to S(131) to obtain a, where S(121) and S(131) are the peak areas of the diffraction peaks of the (211) crystal plane and the (131) crystal plane in the XRD spectrum of the positive electrode active material, respectively.

[0175] In the XRD pattern, the diffraction peak at a diffraction angle of 2θ of 36.1±0.1° is the (121) crystal plane diffraction peak, and the diffraction peak at a diffraction angle of 2θ of 35.3±0.1° is the (131) crystal plane diffraction peak.

[0176] (2) Mass percentage of Ni element in the positive electrode active material:

[0177] Disassemble the empty lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and air dry it at room temperature with humidity ≤15%.

[0178] The positive electrode material is scraped off from the surface of the current collector and calcined at 450℃ for 6 hours to remove the binder and conductive agent, thus obtaining the positive electrode active material.

[0179] A suitable amount (approximately 0.1 g) of the obtained positive electrode active material was dissolved in aqua regia (a mixture of concentrated nitric acid and concentrated hydrochloric acid, with a volume ratio of 3:1, wherein the concentrated nitric acid contains 67% HNO3 by mass and the concentrated hydrochloric acid contains 37% HCl by mass). The solution was heated until completely dissolved and then diluted to 50 mL. An ICP-MS instrument (Thermo Fisher Scientific iCAP PRO X) was used, with the radio frequency power set to 1200 W and the carrier gas flow rate to 0.9 L / min. Ni isotope characteristic mass number 60 was used as the detection target for sample analysis. The Ni content was calculated by comparing the response values ​​of the standard solution and the sample solution, and then the mass percentage of Ni element in the positive electrode active material was calculated accordingly.

[0180] (3) The ratio of lithium manganese iron phosphate agglomerates to the mass of ternary materials

[0181] Disassemble the empty lithium-ion battery to obtain the positive electrode sheet. Soak the positive electrode sheet in DMC (dimethyl carbonate) at room temperature (25℃, the same below) for 60 minutes to remove residual electrolyte and by-products on the surface of the electrode sheet. Take it out and air dry it at room temperature with humidity ≤15%.

[0182] Scrape off the positive electrode material from the surface of the current collector and obtain the mass fraction of elements such as P, Mn, Fe, Ni, Co, and Al (if any) in the positive electrode material by EDS.

[0183] Calculate the mass fraction of LMFP in the cathode material: The chemical formula of LMFP is usually LiMn. x Fe 1-x PO4, where x represents the molar percentage of Mn calculated based on the total molar amount of Mn and Fe in lithium manganese iron phosphate (LMFP). Since EDS yields a mass fraction, an approximate Mn / Fe molar ratio needs to be assumed (e.g., x = 0.5, meaning the molar amounts of Mn and Fe are equal, as an initial calculation value; the actual value may need adjustment based on the specific material). Based on the chemical formula and mass fraction, the total mass fraction of P, Mn, and Fe in LMFP is calculated. This can be done by multiplying the mass fraction of each element by its relative atomic mass ratio in the LMFP chemical formula (considering the number of atoms) and then summing the results.

[0184] Calculate the mass fraction of ternary materials in cathode materials: The chemical formula of ternary materials is usually LiNi. y Co z M (1-y-z)O2, where M is at least one of Mn and Al. Based on the mass fractions of Ni, Co, and Mn obtained from EDS (minus the Mn contribution from LMFP), and the chemical formula of the ternary material, the total mass fraction of Ni, Co, and Mn elements in the ternary material is calculated. Similarly, this requires multiplying the mass fraction of each element by its relative atomic mass ratio in the ternary material's chemical formula (considering the number of atoms), and then summing the results.

[0185] Finally, the total mass fraction of LMFP is divided by the total mass fraction of ternary materials to obtain the mass ratio of lithium manganese iron phosphate agglomerates to ternary cathode materials.

[0186] The performance of the lithium-ion batteries obtained in each embodiment and comparative example was tested. The test results are shown in Table 2. The specific test methods are as follows:

[0187] Peak temperature test: DSC (Differential Scanning Calorimetry). Place the positive electrode in an aluminum or platinum crucible, ensuring a tight seal to prevent volatiles from escaping. Perform temperature calibration using standard substances with known melting points (such as indium, tin, and zinc). Set the starting temperature to 5°C and the ending temperature to 600°C, with a heating rate typically of 5°C / min. Use an inert gas (such as nitrogen) as the test atmosphere. Test equipment: NETZSCH (Germany), model: DSC214;

[0188] Gas generation test during storage: The battery was charged to 4.25V at a constant current (0.2C) using a LAND system. The volume of the fully charged battery was measured using the water displacement method. After drying the battery, it was placed in a 60℃ oven for 42 days. After removing it from the oven, the battery was charged to 4.25V at a constant current (0.2C) using a LAND system, and the volume was measured again using the water displacement method. Gas generation = (volume after storage - initial volume) / battery capacity. The unit of gas generation is mL / Ah.

[0189] Table 2

[0190]

[0191]

[0192] For the batteries prepared in the various embodiments of the present invention, the gas production rate after 42 days of storage at 60°C is ≤8.6mL / Ah, and the peak temperature of the positive electrode is ≤258°C. It can be seen that the batteries containing the positive electrode of the present invention have low gas production and good safety performance.

[0193] Comparing Examples 1-7 with Examples 8-11, and Examples 12-16 with Examples 17-25, it can be seen that when the peak area ratio of the (211) crystal plane to the (131) crystal plane diffraction peak in the XRD spectrum of the positive electrode active material, the mass ratio of Ni element in the positive electrode active material, and the mass ratio of lithium manganese iron phosphate agglomerates to ternary materials meet the preferred range described in this invention, it is more conducive to the balance of gas production and heat production of the battery.

[0194] Comparing Examples 1-7 with Examples 12-16, and Examples 8-11 with Examples 17-25, it can be seen that when the positive electrode sheet satisfies 0.044≤a×b×c<0.110, the battery has a better balance between gas production and heat production.

[0195] According to Comparative Examples 1 and 2, even if the peak area ratio of the (211) crystal plane and the (131) crystal plane diffraction peak in the XRD spectrum of the positive electrode active material, the mass ratio of Ni element in the positive electrode active material, and the mass ratio of lithium manganese iron phosphate agglomerates to ternary materials are all within a suitable range, when the value of a×b×c exceeds the range of 0.004≤a×b×c<0.230, the gas production or heat production of the battery is relatively high, and it is impossible to achieve a balance between gas production and safety performance.

[0196] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this article without departing from the essence and scope of the technical solutions of this article.

Claims

1. A positive electrode plate, characterized in that, The cathode includes a positive current collector and a positive electrode material composited on the positive current collector. The positive electrode material comprises a positive electrode active material, which includes lithium manganese iron phosphate aggregates and ternary materials. The positive electrode sheet satisfies the following conditions: 0.004 ≤ a × b × c < 0.230 Where a is the ratio of the peak area of ​​the (211) crystal plane to the (131) crystal plane in the XRD spectrum of the positive electrode active material, which is dimensionless; b represents the mass percentage of Ni element in the positive electrode active material, which is dimensionless. c is the dimensionless ratio of the mass of lithium manganese iron phosphate agglomerates to the mass of the ternary material.

2. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode plate satisfies: 0.044≤a×b×c<0.

110.

3. The positive electrode sheet as described in claim 1, characterized in that, The range of a is 0.04 to 0.

99.

4. The positive electrode sheet as described in claim 3, characterized in that, The range of a is 0.32 to 0.

99.

5. The positive electrode sheet as described in claim 1, characterized in that, The range of b is 0.004 to 0.

440.

6. The positive electrode sheet as described in claim 5, characterized in that, The range of b is 0.015 to 0.

350.

7. The positive electrode sheet as described in claim 1, characterized in that, The range of c is 0.010 to 99.

000.

8. The positive electrode sheet as described in claim 7, characterized in that, The range of c is 0.428 to 32.

000.

9. The positive electrode sheet as described in claim 1, characterized in that, The ternary material is selected from at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 9.

11. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 10.

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